1. Field of the Invention
The present invention relates to an improved method of chemically generating singlet delta oxygen. It particularly relates to a gas-solid reaction involving a hydrogen halide gas or deuterium halide gas and a solid alkali metal peroxide or solid alkaline earth peroxide.
2. Related Art
The singlet delta (1xcex94g) state of oxygen, its first electronically excited state, lies 7874 cmxe2x88x921 (1.27 microns) above the triplet sigma ground state. Singlet delta oxygen was first discovered in 1924 and has found wide application as an oxidizer1,2 and energy transfer agent3,4. Its role in biological processes5 (cell/tissue destruction, aging and cancer inducing processes), synthetic organic chemistry1,2, airborne environmental and waste treatment chemistry, and the chemical oxygen iodine laser (COIL)3,4,6 is well documented. A variety of methods have been used to produce singlet delta oxygen either from oxygen containing reagents or directly from oxygen. The documented reaction6 used to produce singlet delta oxygen for the COIL is exemplified in equation (1):
2MOH+H2O2(aq)+Cl2xe2x86x92O2(1xcex94g)+2MCl+2H2Oxe2x80x83xe2x80x83(1)
M in equation (1) is an alkali metal or mixture7 thereof The aqueous environment represented by equation (1) is known to deactivate the singlet delta oxygen by collisional quenching and methods for very rapid and efficient oxygen extraction are required for COIL applications8. The hazards associated with concentrated basic hydrogen peroxide are also a disadvantage common to all coil embodiments based upon equation (1) and these hazards necessitate considerations for reaction zone cooling and maximum peroxide utilization and regeneration7,9-12.
A variety of chemical sources of singlet delta oxygen has been reported13. These are typically solution based reactions that include analogs of equation (1). The reaction between gaseous ozone and certain organic substrates in the gas phase leads to singlet delta oxygen formation14. However, this approach is of no practical value in view of the hazards and difficulties associated with producing and handling ozone. Preparative oxidation chemistry methods which utilize singlet delta oxygen are generally limited to substrates soluble in water or in a suitably modified solvent system.
Direct photophysical techniques15 that generate singlet delta oxygen from ground state oxygen require high powered light sources and inconvenient, dangerous pressures (100 atm) in purely gaseous or gas-liquid systems. Microwave or rf discharge of oxygen-gas mixtures are reliable techniques16,17 for producing singlet delta oxygen at low total pressures of ca. 5 torr. A number of possibly undesirable species, including oxygen atoms, are also formed in the discharge process.
1. A. A. Frimer and L. M. Stephenson. The singlet oxygen ene reaction, in Singlet O2, Vol. 2, A. A. Frimer, ed., CRC Press, Boca Raton, Fla., 1984. Ch. 3.
2. R. F. Gould, ed., Oxidation of organic compounds, Vol. 3, Ozone chemistry, photo and singlet oxygen and biochemical oxidations, Advances in Chemistry, Vol. 77 (American Chemical Society, Washington, D.C., 1969.
3. W. E. McDermott, N. R. Pchelkin, D. J. Benard, and R. R. Bousek, An electronic transition chemical laser., Appl. Phys. Lett. 32, 469 (1978).
4. D. J. Benard, W. E. McDermott, N. R. Pchelkin, and R. R. Bousek, Efficient operation of a 100-W transverse-flow oxygen-iodine laser., Appl. Phys. Lett. 34, 40 (1979).
5. A. U. Khan, The discovery of the chemical evolution of singlet oxygen., Int. J. of Quantum Chem. 39, 251 (1991).
6. R. I. Wagner, Singlet delta oxygen generator and process., U.S. Pat. No. 4,310,502, Jan. 12, 1982.
7. C. W. Clendening, W. D. English, M. H. Mach, and T. D. Dreiling, Gas generating system for chemical lasers., U.S. Pat. No. 5,624,654, Apr. 29, 1997.
8. R. A. Dickerson, Singlet delta oxygen generator., U.S. Pat. No. 5,516,502, May 14, 1996.
9. J. D. Rockenfeller, Singlet delta oxygen generator., U.S. Pat. No. 4,461,756, Jul. 24, 1984.
10. W. L. Dinges, Formation of basic hydrogen peroxide., U.S. Pat. No. 5,378,449, Jan. 3, 1995.
11. W. E. McDermott, Singlet delta oxygen generator and process., U.S. Pat. No. 5,417,928, May 23, 1995.
12. D. G. Beshore and D. Stelman, Salt free lithium hydroxide base for chemical oxygen iodine laser., European Patent EP 0 819 647 A2, Jan. 21, 1998.
13. R. W. Murray, Chemical sources of singlet oxygen, in Singlet Oxygen H. H. Wasserman and R. W. Murray, ed., Academic Press, New York, N.Y., 1979, Ch. 3.
14. W. C. Eisenberg, K. Taylor, and R. W. Murray, Gas-phase generation of singlet oxygen by reaction of ozone with organic substances., J. Am. Chem. Soc. 107 8299 (1985).
15. W. C. Eisenberg, Atmospheric gas phase generation of singlet delta oxygen., in Advances in Oxygenated Processes, Vol. 3, pages 71-113, A. L. Baumstark, ed., JAI Press Inc., 1991.
16. S. M. Anderson, J. Morton, K. Mauersberger, Y. L. Yung, and W. B. DeMore, A study of atom exchange between O2(1xcex94) and ozone, Chem. Phys. Lett. 189 581 (1992).
17. J. Schmiedberger and H. Fujii, Radio-frequency plasma jet generator of singlet delta oxygen with high yield, Appl. Phys. Lett. 78, 2649 (2001).
It is, therefore, an object of this invention to provide a technique that produces singlet delta oxygen in high yield from readily available starting materials in a minimally quenching environment without the need for external electrical, optical, or thermal energy.
Another object is to provide a safe method that avoids the use of dangerous, explosive chemicals such as basic hydrogen peroxide.
Yet another object is to provide a process that avoids the need for separating gases from a liquid phase thus rendering it suitable for zero gravity conditions.
A further object is to provide a lightweight, readily scalable, and mechanically simple method that avoids the use of heavy complex machinery, such as vortex mixers, centrifuges, and vacuum pumps to extract excited state oxygen from solution.
To implement the objects stated above, the method of the present invention was devised in which singlet delta oxygen is generated by a chemical reaction at ambient temperature of a solid peroxide with a hydrogen halide gas or a deuterium halide gas, without using external energy sources.
Singlet delta oxygen was produced from an alkali metal peroxide (such as lithium peroxide or sodium peroxide) or an alkaline earth peroxide (such as barium peroxide) in a reaction with a non-radioactive-hydrogen-isotope halide gas (such as hydrogen chloride, hydrogen bromide, deuterium chloride, or deuterium bromide). A static gas fill system was used and the results were observed by emission spectroscopy. Comparable results can be obtained in a flow system, and further, the reaction may take place in a chemical oxygen-iodine laser.
Accordingly, the present invention provides a safe, compact, lightweight, readily scalable, and highly efficient method for producing singlet delta oxygen from commercially available starting materials by directly reacting a solid peroxide with a non-radioactive-hydrogen-isotope halide gas. It avoids the use of unstable starting materials, such as basic hydrogen peroxide that can explode, and liquid phase quenching that can rapidly destroy most of the desired singlet delta oxygen. Furthermore, it avoids the need for a gas-liquid phase separation, thus making it ideal for space-based applications under zero gravity conditions.
The present invention is the chemical generation of singlet delta oxygen by a gas-solid reaction at ambient temperature without external energy sources. A dry, solid alkali metal peroxide or solid alkaline earth peroxide is reacted with a dry hydrogen halide gas or a dry deuterium halide gas to form singlet delta oxygen. Alkali metal peroxides include lithium peroxide, Li2O2, and sodium peroxide, Na2O2; alkaline earth peroxides include barium peroxide, BaO2. Non-radioactive-hydrogen-isotope halide gases include hydrogen chloride, HCl, hydrogen bromide, HBr, deuterium chloride, DCl, and. deuterium bromide, DBr.
All of these materials can be handled safely and are readily available commercially. Furthermore, the reactions of this invention do not require any external energy sources, such as photolysis, discharge, or heat. The desired singlet delta oxygen gas can be generated either in a static or a flow system. In a static system, a suitable peroxide is pressurized with a desired amount of the corresponding hydrogen halide gas or deuterium halide gas, resulting in continuous singlet delta oxygen evolution. In a flow system, a controlled stream of hydrogen halide gas or deuterium halide gas is passed either through a fixed bed of solid peroxide or introduced into a bed of fluidized peroxide, with the latter approach providing increased mixing, conversions, and space utilization. The resulting major products are solid metal halides, water vapor, and singlet delta oxygen gas, O2(1xcex94g), as shown in equation (2) for the reaction of Na2O2 and HCl:
2Na2O2+4HClxe2x86x924NaCl+2H2O+O2(1xcex94g)xe2x80x83xe2x80x83(2)
The preferred peroxides of our invention are alkali metal peroxides and, particularly, lithium peroxide, Li2O2, and sodium peroxide, Na2O2. However, other peroxides, such as alkaline earth peroxides, particularly barium peroxide, BaO2, can also be used in place of the alkali metal peroxides. Further, the reaction may take place in a chemical oxygen-iodine laser.
Among the non-radioactive-hydrogen-isotope halides of our invention, HCl and HBr are preferred, with HBr producing the most intense singlet delta oxygen signals, followed by HCl. Since deuterated compounds quench singlet oxygen to a lesser extent than the corresponding hydrogen analogues, the use of DCl or DBr in place of HCl or HBr, respectively, is of particular interest for this invention. Factors, such as solid surface area and dryness of the starting peroxide may affect these results.
The formation of singlet delta oxygen in our reactions was monitored by the observation of direct emission from the normally forbidden transition of.singlet delta to ground state triplet sigma O2 at 1.27 microns using a liquid nitrogen cooled InGaAs optical multichannel analyzer (OMA) after dispersion with an 0.3 meter spectrograph. The singlet delta oxygen emission signal obtained was identical in wavelength position and contour to that obtained from a microwave discharge of a helium-oxygen mixture at 4 torr and from a small sparger that reacted chlorine gas with basic hydrogen peroxide (BHP) according to equation (1). The sparger contained 100 cc of a mixture that was 7.5 M in H2O2 and 1.1 M in NaOH. The BHP was kept at xe2x88x9210 C and ca. 160 sccm of Cl2 was bubbled through the liquid. A vacuum pump preceded by a liquid-nitrogen cooled trap extracted oxygen from the sparger at 6 torr total pressure. These two techniques are reliable standards for producing quantities of singlet delta oxygen that are readily observable by emission spectroscopy.